Capacitor

ABSTRACT

The manufacture is described of capacitors having a very high capacitance value which is achieved by a very thin dielectric layer, said capacitors being constituted by (i) a layer of nickel or a nickel alloy, (ii) a layer of a cermet adapted to become electrically conductive and containing glass having a melting point less than that of layer (i), and (iii) a layer of a dielectric, said layer (iii) having been formed by chemical interaction of layer (i) with layer (ii) on firing to a temperature at which said interaction takes place, for a time sufficient to produce said layer (iii), the glass content of the cermet being at least 3 percent by weight but insufficient for the cermet itself to act as a dielectric.

[ lMarch 20, 1973 CAPACHTUR [75] Inventor: James Edge, Morpeth, England[73] Assignee: Welwyn Electric Limited, Bedlington, Northumberland,England [22] Filed: June 25, 1971 [21] Appl.N0.: 156,700

Related U.S. Application Data [63] Continuation-in-part of Ser. No.47,767, June 19,

1970, abandoned.

[52] US. Cl. ..317/258, 29/25.42, 117/217, 117/227, 117/70 C [51] int.Cl. ..H01g 1/01 [58] Field of Search ..3 17/258; 117/227, 217, 230,117/70 C; 75/170; 29/25.42

3,386,856 6/1968 Noorlander ..1 17/230 X 3,469,973 9/ 1969 3,523,224 8/1970 3,548,266 12/1970 Frantz ..3l7/258 X Primary Examiner-E. A.Goldberb Attorney-McDougall, Hersh & Scott [5 7 ABSTRACT The manufactureis described of capacitors having a very high capacitance value which isachieved by a very thin dielectric layer, said capacitors beingconstituted by (i) a layer of nickel or a nickel alloy, (ii) a layer ofa cermet adapted to become electrically conductive and containing'glasshaving a melting point less than that of layer (i), and (iii) a layer ofa dielectric, said layer (iii) having been formed by chemicalinteraction of layer (i) with layer (ii) on firing to a temperature atwhich said interaction takes place, for a time sufficient to producesaid layer (iii), the glass [56] References Cited content of the cermetbeing at least 3 percent by UNITED STATES PATENTS geilght butinsufficient for the cermet itself to act as a re ectric. 3,254,9706/1966 Dittrich ..75/17O X 3,353,124 ll/l967 Dilger ..3l7/258 X 9Claims, 5 Drawing Figures REACTION METAL N OR LAYERU////////////////////H7 mm NICKEL ALLOY 2 PATENTEDumzoms 3,721,870

sum 10F 3 MGR U1////[//////////////m NICKEL ALLOY "\4CERMET 5 2-x\\\\\\\\ WWW/MM VENTOR mes Edge M/w MM 02 ATTORNEYS CAPACITANCE(PICOFARAD CM2) PATENTEIJHIR20I073 3,721,870

I szzmznr 3 I 7 I I I I I I I PI 6. 3. 6

FIRING TIME AT 760C (MINS) INVENTOR ATTORNEYS PATEIIIEDIIIR20 ms SHEET 3UT 3 FIG,

SUSPENDING MEDIUM.

F INELY DIVIDED GLASS PARTICLES.

RESISTIVITY IS NOT GREATER THAN 10 ohm cm AFTER FIRING.

KNOWN CERMET COMPOSITION CONTAINING AT LEAST 310 GLASS AND WHOSESPECIFIC CONDUCTIVE METAL AND/OR METAL OXIDE PARTICLES.

FIRING UNDER CONDITIONS NORMALLY APPLIED TO CERMET.

DIELECTRIC LAYER BETWEEN CERMET LAYER AND NICKEL OR NICKEL ALLOY LAYER.

LAYER OF NICKEL OR NICKEL ALLOY.

CAPACITOR The present invention is a continuation-in-part of applicationSer. No. 47,767, filed on June I9, 1970 now abandoned and relates to anovel dielectric, an electrical capacitor having a layer of thedielectric and to methods of making the dielectric and the capacitor.

Resistive cermets are known which, after heating to a high temperature,become electrically conducting. Such known cermets are described, forexample, in the 1968 Hybrid Microelectronics Symposium, pages 173-181,by Darwyn L. Herbst (International Society for Hybrid Microelectronics,October 28-30, 1968, O- Hare lnn, Rosemont, lllinois,); they areresistor pastes which are mixtures of glass frits, metal(s) and/or metalcompounds, usually metal oxides, in a suitable carrier system.

It is known to produce capacitors by firing an oxygen-permeable paintcomposed of a frit containing noble metal particles on to a nickel sheetin such a way that a nickel oxide layer is formed between the paint andthe nickel sheet. This known process depends on the use of a conductingpaint which is permeable to xygen and therefore does not contain anyglass, whereby oxidation of the nickel sheet can occur. According tothis known process, it is also necessary to attach a second contact tothe nickel without the formation of a dielectric layer by theapplication of a conductive glaze which is not permeable to oxygen. Therequired degree of impermeability is achieved by the incorporation ofabout 2 percent of glass (e.g. borosilicate glass) into a conductivesilver composition, so that, on melting, the-glass forms a continuouscoating by sealing the silver particles together.

I have found that if conductive glazes with a glass content of 3 percentor more (preferably at least percent) are used, it is not possible toobtain a good direct contact to nickel, although good contacts can bemade to other metals, e.g. gold. Further investigation of thisunexpected phenomenon has led to the finding that a new dielectric canbe formed as will be described in more detail hereinafter.

It is an object of the present invention to provide a novel dielectricby means of which a very large capacitance value can be obtained.

It is a further object of the present invention to provide a capacitorhaving a very thin dielectric layer whereby the capacitor is endowedwith a large capacitance value.

It is an additional object of the present invention to provide a processfor making capacitors having a very thin dielectric layer.

Further objects of the present invention will become apparenthereinafter.

The present invention provides a capacitor constituted by (i) a layer ofnickel or a nickel alloy, (ii) a layer of a cermet capable of becomingelectrically conductive on firing and containing glass having a meltingpoint less than that of layer (i) (said cermet is wellknown in the art),and (iii) a layer of a dielectric, said layer (iii) having been formedby chemical interaction of layer (i) with layer (ii) on firing to atemperature at which said interaction takes place and for a timesufficient to produce said layer (iii), the glass content of the cermetbeing at least 3 percent by weight but insufficient for the specificresistivity of the cermet itself to exceed 10 ohm centimeter. Theappropriate firing temperature and time for any given layers (i) and(ii) may be easily determined by experiment.

The present invention also provides a dielectric layer formed by thechemical interaction on firing of said layers (i) and (ii).

The present invention further provides a process for making a capacitor,which comprises applying a layer of the above cermet to a layer ofnickel or nickel alloy, and firing the resulting composite article so asto form a third, dielectric layer between said first two layers bychemical interaction thereof, whereby a capacitor is formed.

The present invention additionally provides a process for making thedielectric of the invention which comprises causing chemical reaction totake place by firing the above layers (i) and (ii), whereby thedielectric is formed.

In the capacitor of the present invention the firing causes the cermetto become electrically conductive and causes an insulating film to beformed at the interface between the cermet layer and nickel or nickelalloy (e.g. nickel with boron, nickel with phosphorus or nickel withphosphorus and cobalt) layer; however, the insulating layer produced inthis way is very thin and hence a large capacitance value is obtainedbecause the said insulating layer is essentially defined by the regionof interaction between the nickel or nickel alloy layer, which iselectrically conductive, and the glass in the cermet.

It is thus seen that, in carrying out the process of the presentinvention, the above mentioned dielectric layer is formed at theinterface of two conductive layers (i.e. the nickel or nickel alloylayer on the one hand and the cermet layer on the other hand) by meansof a chemical reaction; the cermet may be applied over the nickel or anickel alloy layer, for example, by means of wellknown screen printingtechniques.

It is known that a thin insulating layer can be produced in a systemconsisting of a coating of an oxygen permeable silver paint applied tothe surface of a sheet of nickel which is then placed in a furnace atabout 900C. Oxygen from the atmosphere permeates the silver layer andthe surface of the nickel sheet in contact with the silver layer isoxidized, thereby forming a thin dielectric film of nickel oxide. Withsuch a technique, it is important to ensure that the high temperatureoxidation treatment is carried out in the presence of an adequate supplyof oxygen (e.g. air) and that the layer of silver paint is uniformlypermeable to oxygen. The properties of the capacitor so formed are thoseof the oxide of the metal constituting the metal sheet to which theoxygen permeable conductive layer is applied.

Although the exact constitution of the dielectric layer of the capacitorof the present invention is not known, test have shown that, unlike thatof the capacitor mentioned in the preceding paragraph, it is not asimple metal oxide formed by a reaction of a metal layer with oxygenfrom the atmosphere. Thus my dielectric layer does not have theundesirable semiconducting properties of nickel oxide and does notdepend on the porosity of an electrode to oxygen for its formation, nordoes it have the considerable thickness which is associated with knownglass like dielectrics when these are applied by relatively simplemanufacturing techniques. My findings are confirmed by the followingevidence.

1. The dielectric of this invention can be produced in an inertatmosphere. For example, using a composition containing a semiconductiveoxide powder produced by burning an alloy of tin and antimony (asuitable such alloy is described in UK. Pat. No. l ,031,65l issued toWelwyn Electric Limited, published June 2, 1966) dispersed with an equalweight of material sold under the designation L92 glass by Glass Tubesand Components Limited, Sheffield Road, Chesterfield, England. Thiscomposition gave capacitors with similar properties when fired in airand in nitrogen at 800C. In both cases the yield and quality were poor.

2. The loss factors of the capacitors produced by my process are betterthan those obtained for nickel oxide capacitors. Furthermore, if thenickel is oxidized before the cermet is fired on to it, electricalproperties of the resulting capacitors are poorer than those ofcapacitors of my invention. For this reason, accidental formation of anoxide layer on the nickel of my capacitors is considereddisadvantageous.

3. Numerous attempts to establish the structure and composition of thecapacitor dielectric have only partly clarified the problem. As pointedout hereinafter, the nickel or nickel alloy film interacts with thecermet during the formation of the dielectric layer to a depth of up toabout 3000 A, but the glass from the cermet is the main ingredient ofthe dielectric layer. The best indication of the composition of thedielectric layer is obtained by examination of a fractured sectionthrough a capacitor using an electron probe analyzer. This shows that,if a layer (ii) of a silver-containing cermet and a layer (i) of nickelare used, the silver and nickel films are divided by a glassy phase.Thus, during firing, the silver and glass in the cermet seem to separateinto layers, possibly due to interaction of the glass with the nickelalloy, leaving a glass as the dielectric.

From the above evidence, I conclude that when nickel interacts with theglass in the cermet, it appears to produce a layer (i.e. the dielectric)into which the conductive phase cannot migrate. This phenomenon suggeststhat, in addition to the chemical reaction, there also takes place theexclusion of the conducting phase due to physical restraint orelectrostatic forces.

The dielectric layer is formed by chemical interaction between the glassin the cermet and the underlying metallic layer (i.e. the nickel ornickel alloy). For this reason, a (i.e. minimum content of glass isnecessary in the cermet and in practice, conductive cermets having atleast 3 percent, preferably 10 percent or more, by weight of glassshould be used. On the other hand, this glass content should not be sohigh that the cermet itself acts as a dielectric. The maximum level ofthe glass content in the cermet depends on the nature of theelectrically conductive phase in the cermet which is used, but it shouldbe such that the specific resistivity of the cermet does not exceed 10ohm centimeter. With a typical cermet thickness of 0.002 centimeter,this upper limit of specific resistivity is obtained when a cermethaving a sheet resistivity of 5 X ohm per square is used. The preferredrange of sheet resistivity for the cermet is from 0.01 ohm per square to10 ohm per square.

As indicated above, the glass in the cermets which may be used in thepresent invention is well known; this glass includes, for example,lead-borate, lead-borosilicate, borosilicate and lead-borobismuthatesystems,

etc.

Typical cermets which have been found to be satisfactory for theformation of dielectric layers by interaction with nickel or a nickelalloy are:

a. Du Pont 7800 Series, supplied by El. Du Pont de Nemours & Co., ofWilmington, Delaware, U.S.A. having a recommended peak firingtemperature of 760C.

. R-l3, R-l4, R-l5 and R-16 paste manufactured by Alloys Unlimited Inc.,and marketed by Kemtron International Ltd., Metropolitan House, VictoriaAvenue, Southend-on-Sea, Essex, England, and recommended for firing at775C.

0. Gold conducting composition C5004, manufactured by Alloys UnlimitedIncorporated and having a recommended firing temperature of 700C.

. A composition comprising 40 percent by weight of Du Pont 7713 silverpaste and percent by weight of powdered X76 glass (the glass being madeby Glass Tubes and Components Limited, Sheffield Road, Chesterfield,England) which is suitably fired at 700C.

Dielectric layers with good electrical properties have been formed byreaction of the above four specific cermets with layers of nickel ornickel alloy (e.g. a nickelphosphorus alloy, nickel-boron alloy or anickelphosphorus-cobalt alloy). When a high temperature firing processis necessary for the cermet, nickel and nickel-phosphorus alloy sufferfrom the disadvantage that any uncoated portions oxidize severely unlessan inert atmosphere is used in the furnace. An alloy of nickel-boron, onthe other hand, does not oxidize as rapidly and temperatures up to themelting point of a nickel-boron alloy may be used for firing cermetsthereon. Dielectric films formed by the interaction of nickel-boronalloy with a conductive cermet have also shown the best capacitorproperties. The nickel-boron alloy film should be of sufficientthickness to give an adequate base electrode even after it has beenpartly chemically reacted with the cermet. The thickness of the nickelor nickel alloy film which interacts with the cermet during theformation of the dielectric film, depending on the duration andtemperature of the firing, can be as great as 3,000 angstrom units; forthis reason, in order to ensure that a metallic electrode layer remains,a capacitor will be formed if the nickel or nickel alloy layer to whichthe cermet is applied is greater than 3,000 angstrom units in thickness.ln prac-.

FIG. 3 represents a plan view of a substrate having capacitors formedthereon in accordance with the process of the present invention,

FIG. 4 is a graph showing curves indicating the variation of thecapacitance with firing times of various capacitors constructed inaccordance with the process of the present invention, and

FIG. 5 is a flow chart illustrating the steps involved in the process ofthe invention.

Referring first to FIG. I of the drawings a substrate I, consisting, forexample, of a sheet of an alumina ceramic material has a film 2 ofnickel alloy, preferably of nickel-boron, deposited thereon. Electrolessplating techniques, well-known in the art, provide one convenient methodof depositing such films. Instead of the substrate of ceramic with thenickel alloy film a single sheet of nickel or a nickel alloy may beprovided. A layer of a cermet 4 (this has a composition such that itbecomes electrically conductive on firing) is applied to the metallicfilm 2 by well-known techniques such as screen-printing; the cermet 4 isthen fired in manner described hereinafter and chemical interaction withthe metal or alloy occurs to form a dielectric layer 3. The cermet layer4, after firing, is essentially conductive, but if its resistivity istowards the upper end of the range specified above, it is preferable toapply a film of a good electrical conductor to enable satisfactoryterminations to be obtained. In order to provide good electricalconnection to the cermet 4, a film 5 of a metal (e.g. aluminum,chromium, nickel, copper, gold or silver) is deposited thereon bywell-known techniques such as, for example, vacuum evaporation.Alternatively a cermet having a high conductivity, e.g. Du Pont 8151palladium-silver paste, may be applied by techniques such asscreen-printing and then fired on to layer 4i.

An alternative form of construction, which makes use of the novelreaction for forming dielectric layers, is illustrated in FIG. 2 of thedrawing. If the nickel alloy film is thin, e.g. nickel-boron alloy ofless than 3,000 angstrom units, so that it all reacts with the cermet,two conducting regions 2 and 4 separated by a narrow dielectric layer 3are obtained. Such narrow layers are useful in the formation ofcapacitors of the interdigitated electrode type, there being appreciablecapacitance between the conducting layers 2 and 4. As described withreference to FIG. I, a metallic film 5 deposited on the surface of thecermet 4 ensures that good electrical connections are achieved.

Using electroless plating techniques, it is more convenient to producethick films of nickel or nickelphosphorus alloy than to deposit thickfilms of nickelboron alloy because nickel-boron plating solutions tendto be less stable than the others. With nickel-boron solutions it isonly possible to maintain relatively low concentrations of boron, in theform of borohydride, in solution with the result that it is difficult todeposit a nickel-boron layer of 80,000 angstrom units thickness sincefrequent additions of small quantities of borohydride have to be made tothe nickel-boron plating solution to avoid exhaustion when long platingtimes are being used. However, very good results may be obtained withnickel-boron alloy but for this purpose it is not necessary that thewhole layer (i) should be of nickel-boron alloy; providing the layer (i)is constituted by a nickel-boron alloy portion of thickness 3,000angstrom units or more, the remainder of said layer may be of nickel ornickel-phosphorus alloy. Such a composite layer (i) may be produced bydepositing on a nickel or nickel-phosphorus alloy layer a nickelboronalloy to a thickness of at least 3,000 angstrom units, the totalthickness being at least 80,000 angstrom units.

When the metallic layer of the capacitor of the invention is anickel-phosphorus or nickel-boron alloy, a suitable upper limit for thephosphorus and boron is 13 percent by weight and 8 percent by weightrespectively, based on the alloy.

FIG. 5 comprises a flow chart illustrating the process steps of theinvention. As indicated, the layer 2 of nickel or nickel alloy isprovided with a layer of a cermet characterized by the propertiesalready discussed. Firing is then carried out at a temperaturerecommended for the cermet employed whereby the dielectric reactionproduct will be formed as the layer 3. A metal film may optionally beadded to provide for electrical connection.

The following Examples are given to illustrate the invention. Referenceis made to FIG. 3 of the drawings which represents a plan view of asubstrate having capacitors produced thereon. In the Examples thecapacitance was measured at a frequency of lKl-Iz.

Example 1 Rosenthal 615X substrates 6 measuring approximately 4.5 X 1.6centimeters were cleaned by immersing them in acetone, then in anultrasonic bath containing a 10 percent solution of Decon marketed byMedical-Pharmaceutical Developments Limited of Ellen Street, Portsladeby Sea, Sussex, and finally rinsed in distilled water. The substrates 6were then immersed for 90 seconds in a beaker containing a sufficientamount of an aqueous solution of 1 percent weight/volume stannouschloride and 1 percent volume/volume hydrochloric acid to just coverthem. The excess solution was poured off the substrates and they werethoroughly rinsed in distilled water. They were then covered for 30seconds with an aqueous solution containing 0.1 percent weight/volume ofpalladium chloride and 0.25 percent volume/volume of hydrochloric acid.The excess solution was poured off and the substrates were rinsed indistilled water having a pH value between 6 and 8.

An aqueous electroless plating solution was prepared having thefollowing composition:

Nickel chloride (hydrated) 283/1, sodium hypophosphite l7g/l, ammoniumchloride g/l and sodium citrate 50gll.

To five parts by volume of this solution was added one part by volume ofan aqueous 20 percent solution of sodium hydroxide.

The activated substrates were immersed in the metallizing solution at80C for 30 minutes during which period of time nickel-phosphorus filmshaving a sheet resistivity of approximately 0.08 ohm per square weredeposited. The metallized substrates were then rinsed in distilled waterand acetone. Some of these metallized substrates were then immersed inan aqueous solution containing,

Nickel chloride (hydrated) 20 g, ethylencdiaminc 50 ml, sodium hydroxide40 g, sodium borohydride 0.67 g distilled water 1 liter for 30 minutesat 80C, during which period a nickelboron layer of at least 3,000angstrom units in thickness was deposited on the nickel-phosphorus film.The metallized substrates were then rinsed in distilled water andacetone. Regions 8, 9, of the substrates, some metallized withnickel-phosphorus and others metallized with nickel-phosphorusoverplated with nickel-boron, were coated with an acid-resistant ink(e.g. KP1093, marketed by Coates Brothers Limited of Easton Street,Rosebery Avenue, London, W.C.l), by known screen-printing techniques anddried at 150C for 30 minutes. The uncoated, i.e. unprotected, regions ofnickel alloy were then etched away using nitric acid and the substrateswere rinsed in distilled water and allowed to dry. The protective inkwas then removed with trichloroethylene. Metallized regions 8, 9 and 10thus remained on the substrates. A film of a paste comprising a mixtureof 90 parts by weight of Du Pont 7822 and 120 parts by weight of Du Pont7823, about 0.002 centimeters thick, was screen-printed on to an area ofthe substrates shown as 7 in FIG. 3 of the drawings. After drying at120C for minutes, the substrates were placed in a furnace at 760C andsamples were removed at intervals up to a maximum of 1 hour. Aftercooling, the substrates were masked so that only the area 7 was exposed.A film of aluminum was vacuum evaporated on to the cermet 7 usingwell-known techniques.

The capacitors so prepared were allowed to stand in air at roomtemperature for about 3 days before measurements were made.

As illustrated in FIG. 3, three capacitors have been provided on eachsubstrate 6, the electrode 7 being common to all three capacitors, theunreacted portions of 8, 9, 10 providing a second electrode for eachcapacitor respectively.

The capacitors so prepared each had an area of 0.064 square centimeters.

The variation in capacitance with firing time at 760C is shown in FIG. 4of the drawings. Curve A shows this variation for the cermet fired on tonickelphosphorus and curve B shows the variation for the cermet fired onto nickel-boron.

For capacitors prepared by interaction of the cermet with nickel-boron,typical values obtained for the loss tangent were: 0.004 at acapacitance value of 1500 picofarads per square centimeter and 0.020 ata capacitance value of 5,500 picofarads per square centimeter. Thesecapacitors exhibited a temperature coefficient of capacitance of lessthan 150 parts per million/C and a typical breakdown voltage of 100 to200 volts. Insulation resistance, measured at room temperature with 1volt D.C. applied, was typically 1.6 X 10" ohm.

Example 2 A sheet of nickel, 0.015 centimeter thick and of purity notless than 99 percent, was degreased by immersion in trichloroethylene. Afilm of Du Pont paste used in Example 1 was applied over an area ofnickel of about 0.1 square centimeter and fired as described inExample 1. A film of aluminum was vacuum evaporated on to the cermet asin Example 1. After allowing to stand for about 3 days at roomtemperature, capacitance values were measured and the variation ofcapacitance with firing time at 760C is shown by curve C in FIG. 4 ofthe drawings. The capacitors produced had an area of about 0.01 squarecentimeters and those of this area with capacitance of 2,000 picofaradper square centimeter had an insulation resistance value (measured atroom temperature at 1 volt D.C.) of about 3.0 X 10 ohm and a value forthe loss tangent of typically 0.020.

Example 3 Substrates 6 were provided with regions 8, 9 and 10 ofnickel-phosphorus alloy coated with nickel-boron alloy, as described inExample 1. A film of Alloys Unlimited Incorporated gold conductorcomposition C5004, about 0.002 centimeters thick, was screen printed onto an area 7. After drying at C for 15 minutes, the substrates wereplaced in a furnace at 700C for 15 minutes and then allowed to cool.Three capacitors, each of 0.064 square centimeters area, were thusproduced on each substrate. The capacitors had a capacitance value ofabout 4,750 picofarad per square centimeter and a value for the losstangent of about 0.005; the insulation resistance, measured at roomtemperature (1 volt D.C. applied) was typically 6.0 X 10" ohm.

Example 4 Capacitorswere prepared as described for Example 3 except thata film of a paste comprising 40 percent by weight of Du Pont 7713 silverconductor composition and 60 percent by weight of powdered (about 5micron particle diameter) X76 glass (the glass being manufactured byGlass Tubes and Components Ltd.) was applied to the nickel-boron alloyand firing was carried out at 700C for 30 minutes.

The capacitors so produced had a capacitance value of about 1900picofarad per square centimeter and the loss tangent was about 0.004;the insulation resistance, measured at room temperature (1 volt D.C.applied), was typically 1.8 X 10 ohm.

Although the present invention is described herein with particularreference to specific details, it is not intended that such detailsshall be regarded as limitations upon the scope of the invention exceptinsofar as included in the accompanying claims.

The L92 glass referred to above has the following composition:

SiO, 56.0 by weight M 0, 1.4 by weight PbO 30.0 I: by weight Na;O 4.6 byweight l(,0 8.0 by weight Example 5 Capacitors were prepared asdescribed for Example 3 except that a film of a paste comprising 52percent by weight of Du Pont 8151 palladium-silver conductor compositionand 48 percent by weight of powdered (about 5 micron particle diameter)X76 glass (manufactured by Glass Tubes and Components Limited) wasapplied to the nickel-boron alloy and firing was carried out at 700C for30 minutes.

The capacitors so produced had a capacitance value of about 1580picofarad per square centimeter and the loss tangent was about 0.007;the insulation resistance, measured at room temperature (1 volt D.C.applied), was typically 5 X ohm. q

The composition of X76 glass used in the above Examples is as follows:

3,0, 17.0 by weight PbO 64.0 by weight ZnO 14.0 by weight SiO, 5.0 byweight.

I claim:

'upon firing, and including a third layer located intermediate saidfirst and second layers, said third layer comprising the reactionproduct resulting from the firing of a composite of said first andsecond layers.

2. A dielectric construction according to claim 1, in

which said first layer is an alloy selected from the class consisting ofnickel-boron alloys, nickel-phosphorus alloys andnickel-phosphorus-coablt alloys.

3. A dielectric construction according to claim 1, in

. which the cermet layer contains at least 10 percent by weight ofglass. I

4. A dielectric construction according to claim 11, in which the cermetused is one having a constitution such that, after firing, it has asheet resistivity of from 0.01 ohm to 10 ohm per square.

5. A construction in accordance with claim 1 wherein terminals areapplied to said'first and second layers whereby the construction isuseful as a capacitor.

6. A capacitor according to claim 5, in which said first layer is analloy selected from the class consisting of nickel-boron alloys,nickel-phosphorus alloys and nickel-phosphorus-cobalt alloys.

7. A capacitor according to claim 5, in which the cermet layer containsat least 10 percent by weight of glass.

8. A capacitor according to claim 5, in which the cermet used is onewhich, after firing, will have a sheet resistivity of from 0.01 ohm to10 ohm per square.

9. A process for producing a construction characterized by dielectricproperties comprising the steps of providing a first layer formed of ametal selected from the group consisting of nickel and alloys of nickel,applying a second layer to said first layer toform a composite, saidsecond layer comprising a cermet capable of becoming electricallyconductive upon firing and having a glass component having a meltingpoint below the melting point of said first layer, said glass beingcontained in said second layer in an amount of at least three percentbyweight but not-exceeding the amount necessary for providing a specificresistivity of the cermet in excess of 10 ohm cm, and firing saidcomposite at a temperature sufficientto producea third layer of adielectric comprising the reaction product developed at the interface ofsaid first and second layers during such firing.

2. A dielectric construction according to claim 1, in which said firstlayer is an alloy selected from the class consisting of nickel-boronalloys, nickel-phosphorus alloys and nickel-phosphorus-coablt alloys. 3.A dielectric construction according to claim 1, in which the cermetlayer contains at least 10 percent by weight of glass.
 4. A dielectricconstruction according to claim 1, in which the cermet used is onehaving a constitution such that, after firing, it has a sheetresistivity of from 0.01 ohm to 106 ohm per square.
 5. A construction inaccordance with claim 1 wherein terminals are applied to said first andsecond layers whereby the construction is useful as a capacitor.
 6. Acapacitor according to claim 5, in which said first layer is an alloyselected from the class consisting of nickel-boron alloys,nickel-phosphorus alloys and nickel-phosphorus-cobalt alloys.
 7. Acapacitor according to claim 5, in which the cermet layer contains atleast 10 percent by weight of glass.
 8. A capacitor according to claim5, in which the cermet used is one which, after firing, will have asheet resistivity of from 0.01 ohm to 106 ohm per square.
 9. A processfor producing a construction characterized by dielectric propertiescomprising the steps of providing a first layer formed of a metalselected from the group consisting of nickel and alloys of nickel,applying a second layer to said first layer to form a composite, saidsecond layer comprising a cermet capable of becoming electricallyconductive upon firing and having a glass component having a meltingpoint below the melting point of said first layer, said glass beingcontained in said second layer in an amount of at least three percent byweight but not exceeding the amount necessary for providing a specificresistivity of the cermet in excess of 106 ohm cm, and firing saidcomposite at a temperature sufficient to produce a third layer of adielectric comprising the reaction product developed at the interface ofsaid first and second layers during such firing.